Buoy with adjustments for the reduction of the effect of the sea forces thereon

ABSTRACT

A buoy specifically constructed for reducing the effect of wave and sea forces thereon. The horizontal diameter of the buoy at the surface of the water is relatively small, with the largest, stabilizing part of the displacement volume of the lower part of the buoy being at a water depth in which the amplitude of the vertical oscillations of the water is smaller than the amplitude movement of the buoy. The stabilizing part of the buoy comprises elongated bodies having an essentially horizontal longitudinal axis.

United States Patent [1 1 Schulze [54] BUOY WITH ADJUSTMENTS FOR THEApr. 17, 1973 3,082,608 3/1963 Daniell ..9/8 P REDUCTIDN OF THE EFFECTOF THE 3,191,202 6/ 1965 Handler ..9/ 8 R SEA FORCES THEREON 3,369,5162/1968 Pierce ..9/8 R [75] Inventor: Hartmut H. O. Schulze, Hamburg,

m y Primary Examiner-Milton Buchler 73 A I H k als N f ldt & K MAssistant Examiner-Gregory W. OConnor 1 sslgnee ifgg: Q ZZ; u eAttorney-Obetlin, Maky, Donnelly & Renner [22] Filed: July 7, 1970 21Appl. No.: 52,844 [571 ABSTRACT A buoy specifically constructed forreducing the effect 30 F A 1i 6 n D m of wave and sea forces thereon.The horizontal diame- 1 m pp ca 0 m y a ter of the buoy at the surfaceof the water is relatively J 18, 1969 Gemlany 19 36 5583 small, with thelargest, stabilizing part of the displace ment volume of the lower partof the buoy being at a 1 [52] 11.8. CL, ..9/8 R water depth in which theamplitude of the vertical II.- C]. Oscillations of the water is Smamerthan the amplitude Field of Search T movement of the buoy. The i i g p fthe buoy comprises elongated bodies having an essentially [56]References cued horizontal longitudinal axis.

UNITED STATES PATENTS 3,159,130 12/1964 Vos ..1 14/05 T 5 Claims, 1Drawing Figure l l 1 I I f I 1 I I: i I T: :1

structions resting on the sea bed are presently used,

where the depth of water allows. In deeper waters, the use of floatingbodies cannot be avoided. In shallow waters, floating bodies arepreferred, on account of the lower costs' Nevertheless, special measuresmust be taken so that these floating bodies, which are hereafterreferred to as buoys, give the greatest possible stability against thesurrounding water surface. Tight anchorage is no use for this, becausethe buoy suddenly loosens, by upward movement against the water surface,which frequently leads to the breaking of the anchorage and the loss ofthe buoy. A rigid fastening of this kind only comes into considerationin the case of underwater floating bodies, which are not, however,usable when the function of the buoy, or the contrivance developed fromit are bound to the water surface. The invention relates only to buoys,and not to buried floating bodies.

The damping of the movement of buoys has already been proposed bydamping plate lying under the surface of the water. These buoys, whichare known as socalled pile buoys, have, however, only a relatively smalldamping effect, inasmuch as the article must not be uneconomicallylarge. They also have the disadvantage that the damping plates, when ina diagonal position, are sensitive to horizontal current, and canproduce considerable, unwanted vertical forces. Also, these dampingcontrivances give no noteworthy resistance to the rolling movement ofthe buoy.

The invention is thus based on the task of creating a buoy of the kinddescribed, which, with moderate construction costs, possesses a goodstability against the accelerating forces of the sea.

The invention rests on two facts. The first is that the acceleratingforces of the sea surface can be traced back chiefly to oscillations inwell-determined frequency and amplitude ranges. These main ranges can,it is true, be very different in different waters, but thy are easy toascertain for a given place. The second fact is that, for thestabilizing of the buoy, the plate shaped construction parts which atfirst sight appear especially well suited, are less appropriate thanelongated bodies, movable transversely in their longitudinal direction,the diameters of such bodies being tuned in a well-determined way to thefrequency rates predominating at any given time. The latter fact wassuggested by the research of Kuelegan and Carpenter on on CylindersForces Plates in an Oscillating Fluid, published in Journal of Researchof the National Bureau of Standards, Washington Vol. 60 No. 5, May 1958.

The solution, therefore, according to the invention, consists in a buoyof the kind described, having the following combination of features:

a. the main part of the displacement volume of the buoy is disposedbelow the water surface in calmer water ranges b. the horizontaldiameter of the portion of the buoy at the surface of the water is smallc. the largest part of the displacement volume of the lower part of thebuoy is laterally adjacent its center of gravity in the form ofelongated bodies with essentially horizontal longitudinal axes and d.the value of UmT/D of these bodies is smaller than 10, where Um is theamplitude of the relative speed between water and the bodies, T the timeof vibration and D the diameter of the bodies.

it has been shown that the lower part of the buoy, in the buoy accordingto the invention, can exert a very high stabilizing force on the buoy,in relation to the construction costs, whereby an excellent resistanceto rolling is also achieved. This success rests in the activation ofhydrodynamic reaction forces, which, by constant counterforce on accountof an assumed depth variation of the floating body, works as a massincrease of the complete oscillating system. This activation of thehydrodynamic reaction forces rests on the tuning, according to theinvention, of the diameter of the elongated bodies of the lower part ofthe buoy to the frequency and height of the waves most prevalent in theparticular area of the sea.

The elongated bodies of the lower part of the buoy are expedientlylinked to a closed ring. The relation of diameter to length isconsequently minimal, so that the best approximation to two dimensionalflow conditions is achieved, which is known to be especially desirable.The closed ring, although preferably circular, can be many sides, forexample triangular or rectangular. It is particularly preferred that theelongated bodies or the ring body have compact cross-sectional form inthe vertical section. The circular section is the most preferred fromthe point of view of dynamic flow; for reason of construction, however,the square or rectangular crosssection, with a side ratio lying near 1,is frequently chosen.

The stabilizing elongated bodies should lie in a depth of water, inwhich the like phase movements of the water on the water surface havediminished in a small amount. And, it is true, the amplitude of the likephase vertical movement of the water surface should be lowered at leastto a fraction which corresponds to the desired reduced mass in relationto the movement of the buoy relative to the movement of the buoy againstthe movement of the water surface. In other words, the stabilizingbodies should lie in a depth of water, in which the amplitude of thevertical oscillations of the water is smaller than the amplitudemovement of the buoy permitted by the corresponding sea.

The distances of the elongated bodies form each other should be, in atransverse direction, such that the flow planes of these bodies are notsubstantially influenced. This consideration determines the minimumdiameter of a stabilizing body formed as a ring body. Whether thediameter is enlarged beyond the minimum diameter depends on the lengthor extent of the ring body necessary for the desired stabilizing effect,and on the desired resistance against rolling movements. If necessary,the diametral distance of the elongated bodies, or the diameter of aring body, can be so proportioned, that the opposite bodies or ringparts he in such depths of water that the accelerating forces working onthem according to phase and/or direction, in comparison with the forcesworking on the buoy near the surface, work in opposition to the buoy. lnprinciple, however, the diametral distance of the elongated bodies, orthe diameter of the the ring body, shouid not be greater than about 20percent of the wave length of the sea principally in consideration.

The invention is more closely described in the following paragraphs withreference to the drawing, which shows in the single FIGURE a schematicside view of a preferred embodiment.

Represented is a buoy, according to the invention, from which aresuspended measuring means for determining horizontal and vertical oceanspeeds for which, therefore, high stability is required.

It consists of a floating body l, which is joined by support legs 2 to aring body 3 having rectangular cross-section which, according to theabove given view points and in agreement with the cited literaturereference, is adjusted with regard to the most frequently met seafrequencies and has a circular out line.

In the middle of the ring body, a ballast tank 4 is pro vided, which inthe sense of the invention is not formed as a stabilizing body, butwhich nevertheless can exert a certain dampening effect. It is joined tothe ring body by struts 9 whereby the distance of the ballast tank fromthe ring body and the struts is so laid out that the hydrodynamicoperation of the ring body is not jeopardized. The oceanographicmeasuring means 5 are hung from a mast 7 by a measuring cable 6. Withthe help of a winch 8 the measuring cable can be raised and lowered.

The cross-section of the floating body 1 at the water line in the rangeof the expected wave heights is held as small as possible with respectto the smallest possible counterforce in relation to the mass of thesystem. The lower limit for this cross-section is determined by theabove-mentioned permissable depth owing to permissable expected loadssuch as ice formations.

v Secondly, the danger of the buoy being cut underneath by strongcurrent requires a not too small cross-section at the water line.

The joining of the floating body with the lower part of the buoy throughthe support legs 2 is necessary, so that in the uppermost water layersmeasurements can be carried out without important disturbance of thewater condition by parts of the buoy. if requirements of this kind donot obtain, the upper and lower parts of the buoy can naturally be heldfast together also in another way.

The buoy is positioned by means of three anchor cables which are set at120 to each other. For this, as may be appropriate, either buoyant ropesor steel cabies with quasi-homogenous distributed buoyancy bodies areused, so that a minimum influence of the anchorage on the oscillatingmovements of the buoy results. The anchoring of buoy should only preventdrifting over a large area, since the construction of the buoy accordingthe the invention affords a sufficient stabilizing effect against thedirect action of the waves.

The center of gravity of the buoy should lie as deep as possible, notfar under the center of displacement. The desired position for thecenter of gravity can be obtained by suitable ballasting of thestabilizing bodies and the ballast tank.

What we claim is: 1. An ad ustable buoy for reducmg the effect of waveand sea forces thereon, -comprising an upper buoy section extendingabove the surface of the water, said upper buoy section being relativelysmall in diameter in the region thereof normally exposed to the waveforce at the surface, a lower buoy section submerged below the watersurface, means for loosely anchoring said buoy to the sea floor, meansfor interconnecting said upper and lower buoy sections, said lower buoysection including a plurality of elongated bodies arranged along agenerally horizontal axis in radially spaced relation relative to thevertical axis of the buoy, the center of gravity of said buoy being Xbut relatively adjacent said horizontal axis of said bodies, the desireddiameter of the bodies being variable depending upon local seaconditions and expressed by the formula wherein Um is the amplitude ofthe relative speed between the water and said bodies, T is the time ofvibration and D is the diameter of said bodies.

2. The buoy of claim 2 wherein said elongated bodies are assembled inthe form of a closed, circular ring.

3. The buoy of claim 2 wherein said closed circular ring has a compactcross-sectional form.

4. The buoy of claim 1 wherein the distance of said elongated bodiesfrom the water line corresponds to a depth of water in which theamplitude of the vertical oscillations of the water in the particularlocal sea environment is less than the permitted amplitude of movementof the buoy in that sea.

5. The buoy of claim 1 1 wherein the transverse distance between saidelongated bodies is such that the flow planes of these bodies are notsubstantially influenced, with such transverse distance not beinggreater than about 20 percent of the expected wave length.

1. An adjustable buoy for reducing the effect of wave and sea forcesthereon, comprising an upper buoy section extending above the surface ofthe water, said upper buoy section being relatively small in diameter inthe region thereof normally exposed to the wave force at the surface, alower buoy section submerged below the water surface, means for looselyanchoring said buoy to the sea floor, means for interconnecting saidupper and lower buoy sections, said lower buoy section including aplurality of elongated bodies arranged along a generally horizontal axisin radially spaced relation relative to the vertical axis of the buoy,the center of gravity of said buoy being X but relatively adjacent saidhorizontal axis of said bodies, the desired diameter of the bodies beingvariable depending upon local sea conditions and expressed by theformula (Um X T)/D <10, wherein Um is the amplitude of the relativespeed between the water and said bodies, T is the time of vibration andD is the diameter of said bodies.
 2. The buoy of claim 2 wherein saidelongated bodies are assembled in the form of a closed, circular ring.3. The buoy of claim 2 wherein said closed circular ring has a compactcross-sectional form.
 4. The buoy of claim 1 wherein the distance ofsaid elongated bodies from the water line corresponds to a depth ofwater in which the amplitude of the vertical oscillations of the waterin the particular local sea environment is less than the permittedamplitude of movement of the buoy in that sea.
 5. The buoy of claim 1wherein the transverse distance between said elongated bodies is suchthat the flow planes of these bodies are not substantially influenced,with such transverse distance not being greater than about 20 percent ofthe expected wave length.